1. Field of Invention
The invention relates to ballasts for gas discharge lamps, particularly of a kind wherein the light output can be controllably maintained at any desired level.
2. Prior Art and General Background
It is well known that significant improvements in overall cost-effectivity can result from appropriately controlling the level of light output from lighting fixtures used for general lighting of offices and the like.
Fluorescent lamp ballasting systems adapted to permit control of light output level on a systems basis presently do exist--as for instance in accordance with U.S. Pat. No. 4,207,498 to Spira et al. However, there are significant complexities associated with practical applications of such light level control systems; and, in spite of the very significant improvements potentially available in cost-effectivity, such light control systems have not gained wide acceptance.
Much of the value available from a light control system may be attained by control of each individual lighting fixture. That way, for instance, light output from each fixture could be kept constant irrespective of any variations in the magnitude of the power line voltage and/or regardless of changes in luminous efficacy of the fluorescent lamp(s) used in the fixture.